Are You Balanced?

Spring/Summer 2008

Jason Erickson

One item often that comes to light during pre-buy and annual inspections is flight control balance. Most aircraft require that the flight controls are balanced within an inch pound spec. If you are buying an aircraft and it has had recent paint or flight control work, be sure it has had the flight control balance checked and an entry stating that it has been performed. If it has not been recorded or the balance results are not made available, you will need to have them checked. Fresh paint on control surface hardware is a tell tale sign that there may be a problem.

Unbalanced flight controls can cause flutter. Results of flight control flutter can be devastating; the percentages of surviving are pretty slim. Google "control surface balance", there are some great resources on the web. It is very important to make sure that changes to flight controls are balanced and your control system is correct. Flutter can be caused by a mis-rigged control system, a bad rod end, loose cables, or other worn components. Maintenance manuals and structural repair manuals all contain allowable balance specifications for required flight controls. Some surfaces range from a few inch pounds to over 30 inch pounds of variation. In other words, some controls can be from a negative two to zero inch pounds, while others are zero to plus 30 inch pounds. The procedure for balance can be a balance bar and one pound weight or simply hanging weight at a specified location in a specified amount. Each aircraft manufacturer has its own procedure and needs to be followed. A balance bench with knife edges is a must for this operation to not only ensure a quality balance, but to keep from damaging the surfaces. Balancing a control surface worth over $40K is always interesting.

At your next inspection, pre-buy inspection, or paint job, make sure that the flight controls are recorded as being checked for balance. This will ensure that the likelihood of control surface flutter is greatly reduced.